# Tagged Questions

A test for comparing the means of two samples, or the mean of one sample (or even parameter estimates) with a specified value; also known as the "Student t-test" after the pseudonym of its inventor.

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### Test for significance of variation in time series data

Suppose a DMV office runs driving tests. Every week a number of people take the driving test, some pass and some fail. Looking at this data set, we notice that the pass rate varies from week to week. ...
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### Is it possible to compare 2 groups while controlling for something?

Is it possible to compare two groups (e.g., t-test, Wilcoxon, Mann-Whitney test, etc.) while controlling for something? E.g., I want to compare home ownership between military veterans and non-...
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### A/B Testing - Risk of excluding guests

I have a sample of 1.6 million users who were split 80/20. 80% of the guests were treated with a message and 20% were shown nothing. ~5% of the guests converted in BOTH populations... but the ...
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### Advance Methods of Understanding Significance of Customer Behaviors

I currently own a couple of websites and lately I've been implementing some feature changes - I've noticed some changes in website traffic and I was wondering what some of the more sophisticated ways ...
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### Not able to understand the intuition behind $z$-test, $t$-test

I am not able to understand and appreciate the basic intuition behind need of this whole hypothesis testing framework, different kinds of tests, looking up tables, significance level etc etc. Why can'...
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### Z-Test and T-test in SPSS custom table - Include 'Total' in comparision

I would like to not only compare columns' proportions and/or means but also each column's proportion and mean against the whole sample (i.e., the 'Total' column). Any way we can obtain that with SPSS ...
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### when dependent variable is categorical with only 2 levels: t-test or chi-square goodness of fit?

Let's say I'm trying to compare if two groups of people are significantly different from each other in terms of their access to the internet. One could code each person's internet access ...
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### multiple paired-sample t-test and Bonferroni Adjustment

I have 4 questionnaires: A,B,C,D. I also have another 4 items ($i_1,i_2.i_3,i_4$) that each measures some aspect of acceptability or feasibility of the questionnaires, which were answered following ...
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### What statistical test can I use?

I'm currently trying to test the effect of pH on the growth of three different types of grasses for my dissertation and didn't account for number of replicates being used (statistically dumb). Here is ...
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### significance between comparisions

I hope this is the right forum for this kind of question (otherwise please point me to the right one). We are working on a RNA-Seq data set (10 biological replica for three conditions). We have ...
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### How to do contrasts in a significant interaction of 2 variables in a 4 four variable set?

I did an analysis of a 2x2x2x2 mixed factorial anova. The first 3 variables were repeated measures and the last was a between groups analysis. The data in the repeated measures were all reaction ...
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### Can I use a paired t-test on data that are averages?

I am comparing 15 pairs of averages paired by two categories with a paired t test. The samples used to determine the averages in each pair are not equal within any single pair of data. For example, if ...
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### Is an independent t-test the right choice for this question?

I was trying to figure out which test I need for analyzing my data. However, I guess by reading that much I confused myself. I analyzed two different retailers with respect to the availability of ...
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### Should I use t-test or ANOVA+post hoc (two different treatments and a control)

I have been working with ice algaes,and Im looking on their fattyacids. Here is a bit about the experimental design. I have one treatment area, cleared, where I have removed all snow. I have ...
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### Simulating probability through random sampling: Is this valid?

What is the name of a simulation that randomly takes two samples from a population and then compares it to another random sample with a predefined condition? I'm writing an assignment and I need some ...
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### Comparing response options ordinal variable single sample

Is there a way to test if the difference between response options of an ordinal variable is statistically significant in a single sample? In my example, we asked 240 survey respondents how well an ...
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### Multiple t tests with Bonferroni correction instead of Anova and posthoc?

I have a set of 6 experiments that were all performed at the same time. This consists of 3 genotypes (A, B, C) , each under two conditions (1 and 2) with a single measurement variable. I just want ...
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### code Welch's t-test in C++ using approximations for student's t values

I need to code a Welch's t-test between two populations in C++ without using external libraries like, for example, boost. I know that given my two populations of size $N_1$ and $N_2$, I can calculate ...
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### Which statistical test should I use to assess the impact of a trial between subjects over time?

In the following table, I'd like to determine if yield is significantly impacted by pesticide application (applied in seasons 7-10) or if the difference between the control field (A) and trial field (...
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### Statistical tests to data organized by weekdays

I have data where there are numeric values (can be 0 also) for corresponding weekdays (1=monday, 2=tuesday, 7=sunday etc). I want to find out if my values (say, for temperature for example) depends on ...
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### Multiple t-tests and interpreting the winner

If you have a question with 3 answer choices and you order them in order of most picked to least pick and run t tests and the top is not sig dif from the middle and the middle is not sig dif from the ...
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### How are independent t-tests affected by unequal Ns?

For example, if I have 11 participants giving one type of response, and 6 participants giving a different type of response. I want to compare the response latency between these two 'groups' of ...
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### What statistical test to use..RM Anova?

I am looking at the effect of darkness on plant stress. I have two treatments (light and dark) with 3 replicates in each treatment. Samples were taken at time points 0 days through to 100 days (0,3,7,...
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### Paired t-test to test trends in regression coefficients between groups

I have data where I estimate regression coefficients/slopes for two groups (e.g. sex-specific regression coefficients) for a number of single effect regression models. I have used Bayesian methods ...
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### Is ANCOVA correct here?

I am analyzing data from a mindfulness intervention in which 60 participants took part in an ipod-based intervention listening to meditation tracks. Outcome measures on anxiety, depression, stress, ...
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### Aggregation of Correlations Coefficients (Spearman)

in an analysis of survey data, I have to deal with multilevel/three-dimensional data. Now, I need to aggregate correlation coefficients found on the individual level (between individual rank-orders) ...
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### Multilevel alternative to Paired t-test

I have a problem where we have N patients, and we measure some property of tumoral lesions for each patient, where the number of lesions varies on each patient (patient A could have 1 lesion, and ...
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### How to compare experimental results of multiple models using significance tests?

I am using 5-fold cross validation to evaluate the errors of 10 models. Therefore, there are 50 results (each model has 5 error values generated from 5 random evaluation partitions). My question is: ...
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### Nested model instead of 5 individual t-tests?

I am trying to compare a test with three replicates to a reference with 9 replicates. My setup is the following: 2 completely different test methods (A, B). Each Method is seperated into 3 ...
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### Derive z- or t-statistic from p-values of regression coefficients from a probit/logit model

I have the results from an empirical study reporting the results for a probit and logit model. They just report the p-values of the regression coefficients. I want to derive the corresponding $t$-/$z$-...
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### Determining two most similar objects based on multiple variables

I am trying to determine the two most similar years based on a number of environmentally variables. For example, I would like to choose the most similar year to 2015, from the set 1989 to 2016, based ...
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### Can I run statistical tests on descriptive statistics like mean and standard deviation? (i.e. no raw data)

I'm trying to figure out which statistical test to run on my data, but it has been processed so that now I have gathered the mean and standard deviation values to be used instead of the raw data. I ...
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### Poisson Regression vs. T-test for Balance

I have many subjects that were cluster-randomized to a treatment group and to a control group. I want to check the age balance of the groups following the randomization - e.g. whether there is a ...
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### statistical test to compare numerical data pre and post intervention

For my research I will be comparing the mean number of screening tests performed before implementation of an intervention and after. The pre and post groups are not the exact same participants. The ...
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### Real-world example on significance testing with large samples

The issues that arise when one uses statistical hypothesis testing framework with large samples are dissussed on CV (see e.g. this thread). The main problem discussed there is that in the real world ...
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### How do I find if two categories of ratio data are different in a manner that is statistically significant?

I have 4 categories of data, A, B, C, and D, that are ratios (market share). Each category has different numbers of records (prescriber-level data). Each record is a market share percentage that is ...
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### one sample t-tests applied to each row - 'data are essentially constant' error

I have three replicates of an experiment which gives me ratios of the abundance of different peptides. If I take the data for one peptide: ...
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### What is it that you're doing when you do a single t test on one predictor of a multiple regression model?

I hope my interpretation is correct. When you're doing a t-test on a single predictor of a multiple regression model, are you looking at how it behaves while the other coefficients are fixed?
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### Paired T-test vs. Survey Design T-Test with Stratification

What is the difference between survey design based approaches to t-tests when there is a stratified sample and paired t-tests where the pairs are the strata? For example, in R there is a svyttest() ...